fix: avoid races in filesystem ops (#2287)

Use `exist_ok` and `missing_ok` in pathlib operations where we can.

cibuildwheel/__main__.py

@@ -399,8 +399,7 @@ def build_in_directory(args: CommandLineArguments) -> None:
 
     output_dir = options.globals.output_dir
 
-    if not output_dir.exists():
-        output_dir.mkdir(parents=True)
+    output_dir.mkdir(parents=True, exist_ok=True)
 
     tmp_path = Path(mkdtemp(prefix="cibw-run-")).resolve(strict=True)
     try:

cibuildwheel/util/file.py

@@ -25,8 +25,7 @@ CIBW_CACHE_PATH: Final[Path] = Path(
 def download(url: str, dest: Path) -> None:
     print(f"+ Download {url} to {dest}")
     dest_dir = dest.parent
-    if not dest_dir.exists():
-        dest_dir.mkdir(parents=True)
+    dest_dir.mkdir(parents=True, exist_ok=True)
 
     # we've had issues when relying on the host OS' CA certificates on Windows,
     # so we use certifi (this sounds odd but requests also does this by default)